The present invention relates generally to substrate processing systems, and, in particular, to isolation valves for substrate processing systems.
Glass substrates are being used for applications such as active matrix television and computer displays, among others. Each glass substrate can form multiple display monitors each of which contains more than a million thin film transistors.
The processing of large glass substrates often involves the performance of multiple sequential steps, including, for example, the performance of chemical vapor deposition (CVD) processes, physical vapor deposition (PVD) processes, or etch processes. Systems for processing glass substrates can include one or more process chambers For performing those processes.
The glass substrates can have dimensions, for example, of 550 mm by 650 mm. The trend is toward even larger substrate sizes, such as 650 mm by 830 mm and larger, to allow more displays to be formed on the substrate or to allow larger displays to be produced. The larger sizes place even greater demands on the capabilities of the processing systems.
Some of the basic processing techniques for depositing thin films on the large glass substrates are generally similar to those used, for example, in the processing of semiconductor wafers. Despite some of the similarities, however, a number of difficulties have been encountered in the processing of large glass substrates that cannot be overcome in a practical way and cost effectively by using techniques currently employed for semiconductor wafers and smaller glass substrates.
For example, efficient production line processing requires rapid movement of the glass substrates from one work station to another, and between vacuum environments and atmospheric environments. The large size and shape of the glass substrates makes it difficult to transfer them from one position in the processing system to another. As a result, cluster tools suitable for vacuum processing of semiconductor wafers and smaller glass substrates, such as substrates up to 550 mm by 650 mm, are not well suited for the similar processing of larger glass substrates, such as 650 mm by 830 mm and above. Moreover, cluster tools require a relatively large door space.
Similarly, chamber configurations designed for the processing of relatively small semiconductor wafers are not particularly suited for the processing of these larger glass substrates. The chambers must include apertures of sufficient size to permit the large substrates to enter or exit the chamber. Moreover, processing substrates in the process chambers typically must be performed in a vacuum or under low pressure. Movement of glass substrates between processing chambers, thus, requires the use of valve mechanisms which are capable of closing the especially wide apertures to provide vacuum-tight seals and which also must minimize contamination.
Furthermore, relatively few defects can cause an entire monitor formed on the substrate to be rejected. Therefore, reducing the occurrence of defects in the glass substrate when it is transferred from one position to another is critical. Similarly, misalignment of the substrate as it is transferred and positioned within the processing system can cause the process uniformity to be compromised to the extent that one edge of the glass substrate is electrically non-functional once the glass has been formed into a display. If the misalignment is severe enough, it even may cause the substrate to strike structures and break inside the vacuum chamber.
Other problems associated with the processing of large glass substrates arise due to their unique thermal properties. For example, the relatively low thermal conductivity of glass makes it more difficult to heat or cool the substrate uniformly. In particular, thermal losses near the edges of any large-area, thin substrate tend to be greater than near the center of the substrate, resulting in a non-uniform temperature gradient across the substrate. The thermal properties of the glass substrate combined with its size, therefore, makes it more difficult to obtain uniform characteristics for the electronic components formed on different portions of the surface of a processed substrate. Moreover, heating or cooling the substrates quickly and uniformly is more difficult as a consequence of its poor thermal conductivity, thereby reducing the ability of the system to achieve a high throughput.
In the past, a variety of isolation valves have been used to isolate two regions from one another. In an exemplary construction, a gate slides into and out of a path, transversely to the path, to open and close the valve. With the gate in a closed position, a seal can be formed between the gate and a valve seat to prevent flow through the valve. Slide valves offer particular compactness, in other words, a small size as measured in a direction along the flow path.
One recently proposed system for processing large glass substrates is a modular in-line processing system, such as the system described in the previously mentioned U.S. patent application Ser. No. 08/946,922. Such a system can be used for CVD or other thermal substrate processing and can include multiple back-to-back processing chambers through which a substrate is transferred. The process chambers typically are operated under vacuum or under very low pressure. Thus, there is a relatively uniform pressure distribution between the chambers which is insufficient by itself to provide the required tight seal between the gate and the valve seat.
In general, the invention discloses various improved isolation valves. According to one aspect, an isolation valve for selectively sealing a first region from a second region includes a housing. The housing defines a channel between the first region and the second region, and the channel extends at least between a first port and a second port. The valve also includes a gate disposed within the housing. The gate is displaceable between a stowed position in which communication is permitted between the first region and the second region, and a deployed position in which the gate spans the channel.
The gate includes first and second sealing members, each of which has a respective outward-facing surface. Further, the gate has an expandable member disposed between the first sealing member and the second sealing member, wherein the expandable member is expandable from a first condition to a second condition and can be contracted from the second condition to the first condition.
In the first condition, the gate is moveable between the stowed and deployed positions. In the second condition, with the gate in the deployed position, the first and second sealing members are biased apart from each other by expansion of the expandable member so that the outward-facing surface of the first sealing member is sealingly engaged to the first port so as to seal the first region from the second region. The outward-facing surface of the second sealing member is engaged to the housing.
In some implementations, such as where two or more processing chambers are positioned back-to-back, both sealing members engage their respective ports to seal the first region from the second region.
In various implementations, the expandable member can include a bellows or an inflatable member, such as an elastomeric bladder.
In another aspect, an isolation valve includes a housing defining a channel between a first chamber and a second chamber and a gate assembly disposed within the housing. The valve also includes means for positioning the gate assembly between a first port in communication with the first chamber and a second port in communication with the second chamber. Additionally, the valve has means for causing the gate assembly to engage the first port so as initially to seal the first chamber from the second chamber. Furthermore, the valve has means for altering a pressure within the housing to further seal the first chamber from the second chamber. A method of sealing a first chamber from a second chamber also is disclosed.
In an alternative embodiment, an isolation valve includes a housing having a passageway through which a substrate can be transferred. A surface along a perimeter of the passageway forms a seat for engaging a gate. The valve also includes a gate disposed within the housing, wherein the gate has a first position in which the passageway is open and a second position in which the gate engages the seat to seal the passageway. The valve also has a lift mechanism coupled to the gate for controlling movement of the gate between its first position and an intermediate position opposite the passageway. The valve also includes a rotating mechanism coupled to the gate for controlling movement of the gate between its intermediate position and its second position.
When the gate is in its second position, a horizontal force component can be provided to seal the gate against the passageway. In one implementation, the rotating mechanism includes one or more push cylinders each having respective first and second positions. Movement of the push cylinders between their first and second positions causes the gate to rotate between its intermediate raised position and its second position in which the passageway is sealed.
In various implementations, two or more substrate processing chambers can be positioned back-to-back. A double-sealing isolation valve or independently controllable isolation valves can be provided between the chambers to seal them, for example, during processing.
The valve housings can be formed separately from the chambers and subsequently secured in place. Alternatively, the valve housings can be formed as a single integral unit with a chamber.
Among the advantages of a valve according to the present invention is design flexibility. For example, in the laboratory or industrial setting, the valve can be used as a door or gate through which glass substrates or other items may pass. In such situations, it is advantageous to select a valve geometry (size, cross-sectional profile, etc.) to accommodate the items passing through the valve as well as any other environmental factors. This is preferable to having to conform the items or processes by which they are manipulated to geometries and sizes of available valves.
By way of example, in the manufacture and processing of flat objects such as glass substrates for flat panel displays, processing chambers may be used which have a relatively low profile, in other words, a small height and large width. Space efficiency considerations indicate that the valves sealing such chambers need only have a similarly low profile to accommodate the ingress and egress of the items.
The use of an inflatable member to separate the valve plates can provide a more even distribution of the sealing force between the valve plates than in a purely mechanical system. Thus, in the case of an elongated gate, the sealing force can be distributed substantially continuously along the gate. However, whatever the desired gate profile, an appropriate inflatable chamber can be configured easily and can use stock inflation equipment. This feature provides cost savings by reducing the need for multiple complex mechanical linkages specifically configured for each gate profile.
Another advantage is the ability to accommodate the valve to less than perfect valve seats. The inflatable member has significant flexibility and, therefore, can create an adequate seal despite a loss of parallelism, changes in seat separation, or even loss of flatness. With a mechanically-actuated valve, wear or contamination of the seating surfaces may greatly alter the forces applied to the plates. With the inflation member, the force is simply related to the pressure applied to the chamber. Performance is less sensitive to wear except in the extreme case of a rupture or leak.
Additionally, to compensate for the lack of ability of the camming mechanism to accommodate changes or irregularities in the seats and to accommodate for the effect of wear of the camming mechanism, a highly compressible flexible seal may be utilized with a cam-type valve. Such a seal will necessarily undergo a relatively high deformation and therefore may be subject to wear or failure. With the present invention, the chamber can provide a significant degree of compliance so that the same compliance need not be present in the seals. Therefore, the seals are subjected to less deformation. The wearing of the mechanical linkages also can create contaminant particles which can interfere with the operation of the valve or the operation of any enclosure the valve is used to seal and contaminate any fluid passing through the valve.
In alternative implementations, mechanical isolation valves are disclosed that are particularly suited for modular systems in which multiple chambers are aligned adjacent one another. Each chamber can be provided with passageways at opposite sides of the chamber. The passageways, which can be used for transferring a substrate into or out of the chamber, can be opened or sealed by respective gates which are controlled independently of one another, thereby providing additional flexibility. The mechanical isolation valves are compact and have a relatively simple construction, thereby helping to reduce manufacturing costs.
The mechanical valves also can provide an improved means for sealing one chamber from another chamber and help prevent cross-contamination from process gases used in the various chambers. The mechanical rotation of the gate toward the passageway creates the seal and provides lateral pressure to improve the seal that is required when processing glass substrates.
When two chambers are aligned adjacent one another, the area between the chambers can be isolated from either one or both of the chamber interiors effectively forming a buffer chamber. The area between the chambers can, therefore, be protected, for example, from process gases, some of which may be corrosive. By isolating the area between the chambers from the chamber interiors, other components of the system external to the processing chambers can be protected from contact with corrosive gases or other harmful materials used within the chambers during substrate processing. Additionally, the pressure of the area between the chambers can be controlled independently of the pressures in either one or both of the chamber interiors.
Other features and advantages will be apparent from the detailed description, drawings and claims.